1. Field of the Invention
The present invention relates to a technique in which a host computer such as a personal computer remotely adjusts a display device or a display monitor connected to the host computer.
2. Description of the Background Art
Known communication technology for adjusting a display monitor remotely from a personal computer (referred to hereinafter as a PC) includes DDC2AB and DCC2BI standards defined by U.S. VESA (Video Electronics Standards Association).
The DDC2AB standard conforms to ACCESS BUS SPEC Ver. 3.0 defined by U.S. ACCESS BUS INDUSTRY GROUP. Under this standard, three signal lines, SDA (Serial Data), SCL (Serial Clock) and GND, are used to transmit commands bidirectionally between the display monitor and the PC. These three signal lines have already been used under VESA DDC2B standard intended for plug and play, and the base protocol thereof conforms to Philips I2C BUS standard. The DDC2B standard is currently used in most PCs and display monitors.
The DDC2BI standard appeared as a subset of the DDC2AB standard, and has a difference to be described below from the DDC2AB standard.
The DDC2AB standard: Both of the PC and the display monitor operate in each of I2C bus master and slave modes.
The DDC2BI standard: The PC always operates only in the I2C bus master mode, and the display monitor operates only in the slave mode.
This creates a large difference to be described below. For the DDC2AB standard which is premised on a multi-master configuration (or a configuration having a plurality of master devices), it is necessary to mount software or hardware for processing such as contention control and the like in each device in order to control the contention between the masters and to support other devices (e.g., a mouse and a keyboard) than the display monitor. For the DDC2BI standard, on the other hand, the contention control is not required since the PC is always the master and the display monitor is always the slave. This simplifies the software and hardware configurations in the PC and the display monitor. For this reason, a large number of DDC2BI-compliant display monitor products are placed on the market at present.
A method of controlling or adjusting the display monitor from the PC based on the DDC2BI standard will be described.
The DDC2BI standard uses a table containing coded control or adjustment items known as VCPs (Virtual Control Panels). The control or adjustment items referred to herein include standardized items related to display monitor screen adjustments such as contrast, brightness, screen position, size and distortion, and related to operation control such as demagnetization, adjustment data storage, gamma characteristic, reset to factory-adjusted conditions. The table also contains an area allocated to define a manufacturer-specific function. The details of these are defined by VESA MCCS (Monitor Control Command Set) standard. The DDC2BI standard basically references the MCCS standard. Some additional definitions are appended in VESA specs (DDC/CI or Display Data Channel Command Interface) which define the MCCS standard.
The VCP is defined also by the aforementioned ACCESS BUS standard and the USB (Universal Serial Bus) standard. A maximum of 256 items ranging from 00h to FFh are definable in the current VCP table. Since the VCP table has reserved areas for use by standard commands, individual manufacturers can freely define and use only 32 areas ranging from E0h to FFh according to the MCCS specs.
For application of the VCP, the DDC2BI standard specifies the following commands:
1) Get VCP Feature
This command from the PC to the display monitor requests the display monitor to send a maximum adjustment data value and a current setting of a specified adjustment item (VCP or Virtual Control Panel) to the PC.
2) VCP Feature Reply
This command is sent from the display monitor to the PC in reply to the Get VCP Feature command and includes information about the maximum adjustment data value and the current setting of the VCP specified by the Get VCP Feature.
3) Set VCP Feature
This command from the PC to the display monitor sets an adjustment data value of the specified adjustment item (VCP or Virtual Control Panel).
4) Save Current Settings
This command from the PC to the display monitor instructs the display monitor to store the current adjustment data in a memory device (EEPROM or the like) in the display monitor.
5) Capabilities Request
This command from the PC to the display monitor requests the display monitor to send a list of VCPs supported by the display monitor and other information to the PC.
6) Capabilities Reply
This command is sent from the display monitor to the PC and includes a response to the Capabilities Request command.
7) Get Timing Report
This command from the PC to the display monitor requests the display monitor to provide information related to timing (frequencies and polarities of horizontal and vertical sync signals) during operation to the PC.
8) Timing Report
This command is sent from the display monitor to the PC and includes a response to the Get Timing Report command (or informs the PC about the frequencies and polarities of the horizontal and vertical sync signals).
An example of operation of an actual application using the above-mentioned commands will be described.
FIGS. 7 and 8 are flowcharts showing part of the operation of an application in the PC. FIG. 9 is a flowchart showing part of the operation of software in the display monitor.
Referring first to FIG. 7, the PC sends the Capabilities Request command to the display monitor in order to identify VCPs supported by the display monitor (Step ST1). Upon receipt of the Capabilities Request command, the display monitor judges that the answer to Step ST20 of FIG. 9 is Yes, and sends, in reply, corresponding VCP codes in ASCII format to the PC in the process of Step ST21. The PC receives a list of the VCP codes supported by the display monitor in the Capabilities Reply receiving process of Step ST2.
Next, the PC sends the Get Timing Report command to the display monitor in Step ST3. Upon receipt of the Get Timing Report command, the display monitor judges that the answer to Step ST22 of FIG. 9 is Yes, and sends in reply the Timing Report to the PC in the process of Step ST23. The PC receives the Timing Report in Step ST4 to receive information about frequencies of horizontal and vertical sync signals at which the display monitor operate and their polarities.
Next, based on the VCP support information received in Steps ST1 and ST2, the PC sends the Get VCP Feature command and receives the VCP Feature Reply for all of the supported VCPs in Steps ST5 to ST7. Then, the display monitor performs corresponding processes in Steps ST24 and ST25.
In Step ST8, the PC performs the process of drawing or creating a control panel screen of a predetermined design for user's external manipulation by means of a mouse and a keyboard. At this time, an item icon and a slide bar are displayed in accordance with the read VCP item and the adjustment data.
In Step ST9, the PC processes an input manipulated by a user by means of the mouse and the keyboard connected to the PC. As a result, if a request occurs for change in adjustment data such as manipulation of the slide bar, the judgment in Step ST10 is Yes. Then, the PC starts a Set VCP Feature command process in Step ST11 to send the Set VCP Feature command to the display monitor. Then, the display monitor recognizes the receipt of the Set VCP Feature command in Step ST26, and changes the internal adjustment data in Step ST27.
If a request to store the adjustment data occurs in Step ST12, the PC starts a Save Current Settings process in Step ST13 to send the Save Current Settings command to the display monitor. Then, the display monitor recognizes the receipt of the Save Current Settings command in Step ST28, and stores the internal adjustment data in an internal memory device (EEPROM or the like) in Step ST29.
In Steps ST14 and ST15, the PC sends the Get Timing Report command and receives the Timing Report command again to monitor the operation timing of the display monitor at regular time intervals (Step ST16). If a change occurs in the operation timing, there is a great possibility that the adjustment data is changed at the same time. Then, the process returns to Step ST5 wherein the PC reads all adjustment data again and repeats its subsequent processes. If it is judged that no change occurs in the operation timing in Step ST16, the process returns to Step ST8, and the PC repeats its subsequent processes.
In the background art DDC2BI-compliant system, individual manufacturers can freely define and use only 32 areas ranging from E0h to FFh in the VCP table, as described above. However, demands have been on the increase for addition of new functions to recent display monitors. For instance, the introduction of digital convergence adjustment and high-precision distortion correction in high-resolution CRT displays allows locally fine adjustments of the screen. There is another demand for adjustment of sound quality and volume and the like resulting from the transmission of an audio signal. Thus, a shortage of the present-day manufacturer-definable areas arises. In this manner, more and more devices are required to expand the VCP table (or cannot meet the demands without the expansion). However, simple VCP expansion, for example, up to 0000-FFFFh will eliminate compatibility with the present standards and therefore be problematic.
Some devices can operate sufficiently with the existing VCP areas. Such devices are adaptable at low costs by managing only the VCPs under the existing standards. Thus, not all devices require the expansion; some require the expansion and others do not.
At present, the DDC2BI standard is also used in some cases when the devices are factory-adjusted. Among factory-adjustable-only items are some items which will cause trouble when accessed by a user. A clear distinction should be made between factory-adjustable items and user-accessible items (open to users). It is risky that the factory-adjustable VCPs use a VCP area (currently available area) which would be defined by the VESA standard in the future. On the other hand, many vendor-defined areas are used for user access, and there is always a shortage of the user-accessible areas, as mentioned above. It is hence also necessary to reserve the factory-adjustable-only VCP areas.